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The Lymphatic System and Body Defenses

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1 The Lymphatic System and Body Defenses

2 The Lymphatic System Consists of two semi-independent parts
Lymphatic vessels Lymphoid tissues and organs Lymphatic system functions Transport fluids back to the blood Play essential roles in body defense and resistance to disease

3 Lymphatic Characteristics
Lymph – excess tissue fluid carried by lymphatic vessels Properties of lymphatic vessels One way system toward the heart No pump Lymph moves toward the heart Milking action of skeletal muscle Rhythmic contraction of smooth muscle in vessel walls

4 Lymphatic Vessels Lymph Capillaries
Walls overlap to form flap-like minivalves Fluid leaks into lymph capillaries Capillaries are anchored to connective tissue by filaments Higher pressure on the inside closes minivalves

5 Lymphatic Vessels Figure 12.2

6 Lymphatic Vessels Lymphatic collecting vessels
Collects lymph from lymph capillaries Carries lymph to and away from lymph nodes Figure 12.1

7 Lymphatic Vessels Lymphatic collecting vessels (continued)
Returns fluid to circulatory veins near the heart Right lymphatic duct Thoracic duct Figure 12.1

8 Lymph Materials returned to the blood Water Blood cells Proteins

9 Lymph Harmful materials that enter lymph vessels Bacteria Viruses
Cancer cells Cell debris

10 Lymph Nodes Filter lymph before it is returned to the blood
Defense cells within lymph nodes Macrophages – engulf and destroy foreign substances Lymphocytes – provide immune response to antigens

11 Lymph Nodes Figure 12.3

12 Lymph Node Structure Most are kidney-shaped, less than 1 inch long
Cortex Outer part Contains follicles – collections of lymphocytes Medulla Inner part Contains phagocytic macrophages

13 Lymph Node Structure Figure 12.4

14 Flow of Lymph Through Nodes
Lymph enters the convex side through afferent lymphatic vessels Lymph flows through a number of sinuses inside the node Lymph exits through efferent lymphatic vessels Fewer efferent than afferent vessels causes flow to be slowed

15 Other Lymphoid Organs Several other organs contribute to lymphatic function Spleen Thymus Tonsils Peyer’s patches Figure 12.5

16 The Spleen Located on the left side of the abdomen Filters blood
Destroys worn out blood cells Forms blood cells in the fetus Acts as a blood reservoir

17 The Thymus Located low in the throat, overlying the heart
Functions at peak levels only during childhood Produces hormones (like thymosin) to program lymphocytes

18 Tonsils Small masses of lymphoid tissue around the pharynx
Trap and remove bacteria and other foreign materials Tonsillitis is caused by congestion with bacteria

19 Peyer’s Patches Found in the wall of the small intestine
Resemble tonsils in structure Capture and destroy bacteria in the intestine

20 Mucosa-Associated Lymphatic Tissue (MALT)
Includes: Peyer’s patches Tonsils Other small accumulations of lymphoid tissue Acts as a sentinal to protect respiratory and digestive tracts

21 Body Defenses The body is constantly in contact with bacteria, fungi, and viruses The body has two defense systems for foreign materials Nonspecific defense system Specific defense system

22 Body Defenses Nonspecific defense system
Mechanisms protect against a variety of invaders Responds immediately to protect body from foreign materials Specific defense system Specific defense is required for each type of invader Also known as the immune system

23 Body Defenses Figure 12.6

24 Nonspecific Body Defenses
Body surface coverings Intact skin Mucous membranes Specialized human cells Chemicals produced by the body

25 Surface Membrane Barriers – First Line of Defense
The skin Physical barrier to foreign materials pH of the skin is acidic to inhibit bacterial growth Sebum is toxic to bacteria Vaginal secretions are very acidic

26 Surface Membrane Barriers – First Line of Defense
Stomach mucosa Secretes hydrochloric acid Has protein-digesting enzymes Saliva and lacrimal fluid contain lysozyme Mucus traps microogranisms in digestive and respiratory pathways

27 Defensive Cells Phagocytes (neutrophils and macrophages)
Engulfs foreign material into a vacuole Enzymes from lysosomes digest the material Figure 12.7a

28 Events of Phagocytosis
Figure 12.7b

29 Defensive Cells Natural killer cells Can lyse and kill cancer cells
Can destroy virus- infected cells

30 Inflammatory Response - Second Line of Defense
Triggered when body tissues are injured Produces four cardinal signs Redness Heat Swelling Pain Results in a chain of events leading to protection and healing

31 Functions of the Inflammatory Response
Prevents spread of damaging agents Disposes of cell debris and pathogens Sets the stage for repair

32 Steps in the Inflammatory Response
Figure 12.8

33 Antimicrobial Chemicals
Complement A group of at least 20 plasma proteins Activated when they encounter and attach to cells (complement fixation) Figure 12.10

34 Antimicrobial Chemicals
Complement (continued) Damage foreign cell surfaces Has vasodilators, chemotaxis, and opsonization Figure 12.10

35 Antimicrobial Chemicals
Interferon Secreted proteins of virus-infected cells Bind to healthy cell surfaces to inhibit viruses binding

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